Nginx High Availability – How to Set Up Reverse Proxy for Failover

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The scenario is like this, I have a nginx reverse proxy server in front of two app servers which are backups of each other, I want nginx to forward all user requests to the first app server at first, and if the first app server is down, I want nginx to forward all user requests to the second app server from that time on, until if the second app server is down, and nginx should revert back to forward all user requests to the first app server, so on and so forth. Of course, if both app servers are down then nginx will return an error.

I looked into settings like upstream load balancing and proxy_next_upstream settings but it seems not really what I'm looking for here. Any idea how to configure nginx for my scenario? Thanks.

Best Answer

You'll want to be using the nginx upstream configuration in order to achieve this..

upstream mybackend {
    # first app server
    server 192.168.0.1;

    # second app server
    server 192.168.0.2 backup;
}

server {
    ...

    location / {
        proxy_pass http://mybackend;
    }
}

The key here is the backup parameter, which tells nginx to only utilize that node in the event that primary nodes (i.e; nodes not tagged backup) are unavailable.

Full documentation here.

Related Solutions

Nginx – How to Set Up as a Caching Reverse Proxy

I don't think that there is a way to explicitly invalidate cached items, but here is an example of how to do the rest. Update: As mentioned by Piotr in another answer, there is a cache purge module that you can use. You can also force a refresh of a cached item using nginx's proxy_cache_bypass - see Cherian's answer for more information.

In this configuration, items that aren't cached will be retrieved from example.net and stored. The cached versions will be served up to future clients until they are no longer valid (60 minutes).

Your Cache-Control and Expires HTTP headers will be honored, so if you want to explicitly set an expiration date, you can do that by setting the correct headers in whatever you are proxying to.

There are lots of parameters that you can tune - see the nginx Proxy module documentation for more information about all of this including details on the meaning of the different settings/parameters: http://nginx.org/r/proxy_cache_path

http {
  proxy_cache_path  /var/www/cache levels=1:2 keys_zone=my-cache:8m max_size=1000m inactive=600m;
  proxy_temp_path /var/www/cache/tmp; 


  server {
    location / {
      proxy_pass http://example.net;
      proxy_cache my-cache;
      proxy_cache_valid  200 302  60m;
      proxy_cache_valid  404      1m;
    }
  }
}

Nginx failover without load balancing

What you want is an active+passive setup. Here's an example nginx conf snippet to get you going:

upstream backend {
    server 1.2.3.4:80 fail_timeout=5s max_fails=3;
    server 4.5.6.7:80 backup;
}

server {
    listen 80;
    server_name whatevs.com;

    location / {
        proxy_pass http://backend;
    }
}

So, 'normally', all requests will go to host 1.2.3.4. If we get three failures to that box, then 4.5.6.7 will take over.

Best Answer

Related Solutions

Nginx – How to Set Up as a Caching Reverse Proxy

Nginx failover without load balancing

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